Data storage systems can occasionally corrupt data. These corruptions occur for several reasons. For example, firmware bugs, unprotected cache memories, bus errors can cause bits in data blocks to be modified. Such errors are “silent” because the data storage system does not realize that the error has occurred. Silent data corruption may create significant problems. For example, when an application requests data and gets the wrong data, the application may crash, or alternatively, the application may pass along the corrupted data to other applications.
Silent data corruption is especially troublesome when it occurs in streaming media devices such as tapes. The streaming media devices, traditionally used for backup, are typically written once and not read again until an emergency occurs. If a streaming media device suffers a silent data corruption, systems that will subsequently use backup copies retrieved from the affected tape to recover data may from then on be unknowingly operating on corrupted data. Such situations may have disastrous consequences (e.g., irreparable undetected long-term data corruption).